In conventional 3GPP technical specification of Rel-8 or Rel-9, two kinds of radio resource measurement need to be performed by a User Equipment (UE), one is radio link monitoring (RLM) measurement, and the other one is Radio Resource Management (RRM) measurement. A specific measurement process is described in 3GPP TS 36.133 v8.11.0 and TS 36.133 v9.5.0.
The RLM measurement is performed when the UE needs to monitor the downlink quality of a serving cell to report an out-of-sync or in-sync state to a higher layer. The UE monitors the downlink quality of the serving cell based on a Cell-specific Reference Signal (CRS).
In the RLM measurement, the UE needs to estimate the downlink quality, and then compares the downlink quality with threshold values Qout and Qin, so as to evaluate the downlink quality of the serving cell. The threshold value Qout is defined as a channel quality level at which the downlink can not be received reliably, and the threshold value Qin is defined as a channel quality level at which the downlink can be received accurately.
In a non-Discontinuous Reception (non-DRX) mode, the physical layer (Layer 1) of the UE needs to evaluate the channel quality of the last period every radio frame of 10 ms and compare the channel quality with the threshold values Qout and Qin. When the evaluated channel quality is lower than the threshold value Qout, the physical layer of the UE needs to report out-of-sync to a higher layer. When the evaluated channel quality is higher than the threshold value Qin, the physical layer of the UE needs to report in-sync to the higher layer.
In each radio frame, when the downlink quality evaluated every period of 200 ms is lower than the threshold value Qout, the physical layer of the UE transmits an out-of-sync indication to the higher layer. In each radio frame, when the downlink quality evaluated every period of 100 ms is higher the threshold value Qin, the physical layer of the UE transmits an in-sync indication to the higher layer. The out-of-sync and in-sync evaluation should meet a condition that the interval of two continuous physical layers is 10 ms at least.
In a DRX mode, the physical layer of the UE needs to evaluate the channel quality of the past period every DRX period and compare the channel quality with the threshold values Qout and Qin. When the evaluated channel quality is lower than the threshold value Qout, the physical layer of the UE needs to report out-of-sync to the higher layer. When the evaluated channel quality is higher than the threshold value Qin, the physical layer of the UE needs to report in-sync to the higher layer.
In the DRX mode, the evaluation period of Qout (TEvaluate_Qout_DRX) and the evaluation period of Qin (TEvaluate_Qin_DRX) are defined in Table 1.
TABLE 1the evaluation periods of Qout and Qin in the DRX modeTEvaluate_Qout_DRX andThe length of DRXTEvaluate_Qin_DRX (s) (theperiod (s)number of DRX periods)≦0.04[Note (20)]0.08[0.8 (10)]0.16[1.6 (10)]0.32[3.2 (10)]0.64[6.4 (10)]1.28[6.4 (5)]2.56[12.8 (5)]Note:the evaluation period is dependent on the length of the DRX period in the DRX mode.
The UE needs to perform RRM measurement to identify a neighbor cell, and performs Reference Signal Receiving Power (RSRP) measurement or Reference Signal Receiving Quality (RSRQ) measurement for the identified neighbor cell. In a shared-frequency RRC_CONNECTED state, the UE needs to perform continuous RRM measurement for the identified cell, and search for some new cells.
In the non-DRX mode, a measurement period of performing shared-frequency RSRP and RSRQ measurement by the UE is 200 ms. In the measurement period, it is related to an implementation that the UE performs RSRP or RSRQ measurement on which sub-frame, and the specification does not limit the measurement on a sub-frame of a non-Multicast Broadcast Single Frequency Network (non-MBSFN).
TABLE 2the measurement period of RRM of shared-frequency cell in the DRX modeThe length of DRXTmeasure_intra (s) (theperiod (s)number of DRX periods)≦0.040.2 (Note 1)0.04 < DRX-cycle ≦ 2.56(Note 2) (5)(Note 1):the number of DRX periods is dependent on the length of the DRX period in the DRX mode.(Note 2):the measurement period is dependent on the length of the DRX period in the DRX mode.
In the measurement period, it is related to an implementation that the UE performs RSRP measurement or RSRQ measurement on which sub-frame, and the specification does not limit the measurement on a sub-frame of the non-MBSFN.
For an event-driven measurement report, when a measurement report condition is met, the UE will transmit an event-driven measurement report.
In an idle mode, the UE needs to perform RRM measurement for the current cell and neighbor cells every DRX period, to measure the current cell and identify the neighbor cells. If the signal strength or RSRQ of the current cell and a neighbor cell meets a certain condition, the UE performs cell reselection to select the measured neighbor cell as a new resident cell.
In current 3GPP, as a technical solution which can greatly improve system throughput and whole network efficiency, a Heterogeneous Network (Hetnet) formed by different power nodes in the same covering area in Long Term Evolution (LTE) and LTE-Advanced (LTE-A) attracts much attention. In March, 2010, a work project of Enhanced Inter-cell Interference Coordination (eICIC) for HetNet is set up.
The eICIC for HetNet is a technical solution which can greatly improve system throughput and whole network efficiency. The Heterogeneous Network is a heterogeneous system which is formed by different types of nodes in the same covering area by configuring Low Power Nodes (LPNs) in a covering area of a Macro Node B. The LPNs include a Pico Node B and a Home Node B (HNB).
An important problem in the Heterogeneous Network is interference between the nodes in the same covering area, especially the transmission power of the Macro Node B is much larger than that of the LPN, which results in interference of the Macro Node B on the downlink receiving of boundary users in the LPN and interference of a large power node at the boundary of the Macro Node B on a neighbor LNP. In addition, in a scenario in which the Home Node B controls a Closed Subscriber Group (CSG), the transmission of the Home Node B will result in large interference on users of a neighbor Macro Node B.
In the discussion on 3GPP, many interference coordination technologies are put forward, e.g., resource division and power control technologies. The interference coordination of time domain is an important method, which can avoid that the Macro Node B and the LPN transmit data on the same sub-frame at the same time. The data transmission of one node can be limited on some sub-frames, so as to decrease interference on users served by the other one node.
In a Macro Node B-Home Node B scenario, a UE under the Macro Node B in a non-CSG will be interfered greatly when the UE approaches some Home Nodes B in the CSG, as shown in FIG. 1. FIG. 1 is an interference diagram in a Macro Node B-Home Node B scenario.
In the scenario shown in FIG. 1, users under the Macro Node B in the covering area of Home Node B 1 cannot correctly receive control information and data unless some eICIC methods are used.
The eICIC method of time domain includes that the Home Node B generates some Almost Blank Sub-frames (ABSes) through some special scheduling, that is, the HNB generates sub-frames with little interference, and then the control information and data of the users under the Macro Node B only can be scheduled on those sub-frames with little interference, so as to guarantee that the control information and data of the users under the Macro Node B can be received correctly.
Similarly, when the Macro Node B greatly interferes with the user of the LPN, e.g. a Pico Node B, those ABSes also can be applied to the Macro Node B, as shown in FIG. 2. FIG. 2 is an interference diagram of a Macro Node B-Pico Node B scenario.
In FIG. 2, the Macro Node B transmits data only on sub-frames 0, 2, 5, 8 and 9, and does not transmit data on sub-frames 1, 3, 4, 6 and 7, which are ABSes. In this way, the Pico Node B only makes the users at the boundary of a Pico cell transmit downlink data on the sub-frames 1, 3, 4, 6 and 7, so as to avoid the interference of the Macro Node B on the users at the boundary of the Pico cell.
According to the discussion on 3GPP, if RLM measurement or RRM measurement is performed according to a RLM measurement process in LTE Rel-8 or Rel-9 or according to a RRM measurement process in LTE Rel-8 or Rel-9, the UE does not differentiate ABSes and non-ABSes, but performs the RLM measurement or the RRM measurement, which will result in unnecessary radio Link Failure (RLF) processing and switching. The RLM measurement process and the RRM measurement process in LTE Rel-8 or Rel-9 are methods described in 3GPP TS 36.133 v8.11.0 and TS 36.133 v9.5.0.
And thus, in the current discussion on 3GPP, a resolution points out that in a Macro Node B-Home Node B scenario and a Macro Node B-Pico Node B scenario, a serving cell of the UE will make the UE perform the RLM measurement or the RRM measurement on restricted resources, so as to avoid the Radio Link Failure processing and switching.
For example, in the Macro Node B-Home Node B scenario shown in FIG. 1, the Home Node B transmits data to a UE under the Home Node B only on sub-frames 0, 2, 5, 8 and 9, and the Macro Node B schedules data transmission for a UE neighbor to the Home Node B on sub-frames 1, 3, 4, 6 and 7, because the sub-frames 1, 3, 4, 6 and 7 correspond to ABSes of the Home Node B. Since the UE under the Macro Node B performs RLM measurement or RRM measurement only on the sub-frames 1, 3, 4, 6 and 7 or a subset of the set of these sub-frames, the measured interference is much smaller than the interference obtained based on the RLM measurement or RRM measurement in LTE Rel-8 or Rel-9, and a measurement result obtained by performing RLM measurement or RRM measurement on the sub-frames 1, 3, 4, 6 and 7 or the subset of the set of these sub-frames can correctly reflect an actual state of the UE. Thus, the UE under the Macro Node B should perform the RLM measurement or the RRM measurement on the restricted resources, that is, perform the RLM measurement or the RRM measurement on the sub-frames 1, 3, 4, 6 and 7 or the subset of the set of these sub-frames.
However, when the UE under the Macro Node B performs RLM measurement or RRM measurement on the restricted resources, there are following problems.
When UEs under the Macro Node B move in the covering area of the Macro Node B, most UEs do not pass by the covering area of the Home Node B. In this case, if all UEs are configured to perform RLM measurement or RRM measurement on the restricted resources, the measurement precision will be decreased because performing measurement on the restricted resources means the decrease of the measured samples. In addition, if it is necessary to guarantee the measurement precision, an additional measurement process or measurement value processing process needs to be added, which will result in the complexity of the RLM measurement or RRM measurement.
In addition, according to the current conclusion of 3GPP, in the Macro Node B-Home Node B scenario, there is no Backhaul coordination between the Macro Node B and the Home Node B. Thus, when the ABS configured by the Home Node B changes, the Home Node B can not notifies the Macro Node B instantly.
Therefore, it is necessary to provide an improved method, to improve the measurement precision of the RLM measurement and RRM measurement in the Heterogeneous Network, so as to decrease the complexity of the RLM measurement and RRM measurement and guarantee system stability.